Cambridge public health officials announced on September 23 that the Charles River, spanning the border between Cambridge and Boston, is now safe for direct contact. State-conducted water testing revealed cyanobacteria concentrations below levels considered a health risk, prompting the department to lift the advisory that had barred touching the river.
The advisory was originally put in place earlier this summer after officials warned of toxin‑producing microorganisms in the water. Those warnings led to a temporary closure of the river for recreational contact while testing and monitoring were conducted.
Cyanobacteria, often called blue‑green algae, can produce toxins that affect skin and respiratory health when present in high amounts. State laboratories assess water samples against established thresholds; levels below those thresholds are deemed not hazardous to the public. The recent tests showed the river’s cyanobacterial counts were comfortably under the concern level.
With the advisory now removed, residents and visitors can again engage in activities that involve direct contact with the river, such as wading, kayaking, or simply touching the water. The Cambridge Public Health Department emphasized that the decision reflects current conditions and that the river remains under regular surveillance.
Officials said they will continue periodic testing throughout the season to ensure cyanobacteria levels remain low. The department encouraged the public to stay informed about any future advisories that may arise should water quality change.